1. Field of the Invention
The present invention relates to a housing for an electronic apparatus such as a server of a work station, and more particularly to a housing having an electromagnetic wave leakage preventing function.
2. Description of the Related Art
It is sometimes demanded that a housing for an electronic apparatus have a function of preventing radiation to the outside of electromagnetic waves generated from electronic parts, electronic circuits and so forth accommodated in the housing. In order to satisfy the demand, it is a conventional countermeasure to establish electric connection at a fitting location between a plurality of metal plates which form a housing.
FIG. 3 is a perspective view showing part of a conventional housing, and FIG. 4 is an exploded view of the portion of the housing shown in FIG. 3. Referring to FIGS. 3 and 4, the conventional housing shown includes a bottom plate (not shown), a top plate 101 disposed in parallel to the bottom plate, and a pair of side plates 102 attached to the opposite edges of the bottom plate and the top plate 101. The bottom plate, top plate and side plates are all metal plates.
FIG. 5 is a perspective view showing an end portion of the top plate 101. A coupling edge portion 106 for coupling the top plate 101 to a side plate 102 is provided on a side edge of the top plate 101. The coupling edge portion 106 is formed as a unitary member including a vertical first portion 106a bent downwardly in an L-shape from the side edge of the top plate 101, a horizontal second portion 106b bent in an L-shape toward the inner side of the housing from the first portion 106a, and a vertical third portion 106c bent downwardly in an L-shape from the second portion 106b and extending in parallel to the first portion 106a. A plurality of horizontally elongated fitting slots 103 each tapering toward one end thereof are formed at different locations of an upper portion of the third portion 106c. Further, a plurality of contact portions 105 are formed together with recesses at portions of the third portion 106c below the fitting slots 103. An end portion of each of the contact portions 105 is bent to the outer side, and a circular projection 104 is provided on an outer face of an end portion of the bent portion. The outer face of the third portion 106c below a boundary between the fitting slots 103 and the contact portions 105 is formed as a non-coated face which is not coated, but the outer face of the third portion 106c above the boundary is colored by coating including the second portion 106b and the first portion 106a as well as the top face of the top plate 101. The coated portions are indicated by intersecting slanting lines.
Meanwhile, a horizontal coupling edge portion 102b bent in an L-shape is formed on the top edge of each side plate 102 as shown in FIG. 4, and a plurality of fitting pawls 102a are formed in an upwardly projecting manner at different locations of the coupling edge portion 102b. While the outer face of each of the side plates 102 is colored by coating including the outer face of the coupling edge portion 102b, the inner face of each of the side plates 102 is not coated including the inner face of the coupling edge portion 102b. 
The top plate 101 and each side plate 102 are coupled to each other in the following manner. As shown in FIG. 4, the fitting pawls 102a of the side plate 102 are inserted into the fitting slots 103 of the top plate 101 and slidably moved to the tapering end side of the fitting slots 103 so that the fitting pawls 102a are fitted with the fitting slots 103 to couple the top plate 101 and the side plate 102 to each other. At this time, since the projections 104 project to the outer side farther than the base portion of the third portion 106c, they contact with the inner face of the side plate 102. Since the inner face of the side plate 102 is not coated, electric connection is established between the top plate 101 and the side plate 102.
It is to be noted that the opposite side edge portion of the top plate 101 and the other side plate 102 are joined together by a similar mechanism. Also the bottom plate and the side plates 102 are joined together by similar mechanisms.
Accordingly, radiation of electromagnetic waves from electronic parts, electronic circuits and so forth accommodated in the housing can be prevented by the entire housing.
FIGS. 6 and 7 show a top plate of another conventional housing. Referring to FIGS. 6 and 7, the top plate 110 of the conventional housing shown includes a metal plate 110a whose side edge portion 10b is bent downwardly in an L-shape. A conductive plate 110c having an L-shaped cross-section is secured by welding or the like to the inner side of the side edge portion 110b. A plurality of fitting slots 103 similar to those shown in FIG. 5 are formed at different locations of an upper portion of an exposed outer face of the side edge portion 110b. A plurality of contact portions 105 each having a projection 104 thereon are formed on the side edge portion 110b of the conductive plate 110c below the fitting slots 103. It is to be noted that, although the outer face of the metal plate 110a is colored by coating, the inner face of the metal plate 110a is not coated. The coated portions are indicated by intersecting slanting lines in FIG. 6. Further, the conductive plate 110c is not coated so that electric connection is established between the metal plate 110a and the conductive plate 110c. 
Accordingly, also where the top plate 110 described is used, since the top plate 110 and a side plate are coupled to each other in a similar manner as in the conventional housing described hereinabove, radiation of electromagnetic waves from an electronic apparatus in the housing can be intercepted by the entire housing.
However, where the conventional top plate 101 shown in FIG. 5 is produced, if the contact portions 105 are coated, then since establishment of electric connection thereof to the side plates 102 becomes impossible, it is necessary to perform coating of a metal plate, which is to make the top plate 101, while the other portion than the intersecting slanting line portion in FIG. 5 is held masked. On the other hand, where the conventional top plate 110 shown in FIG. 6 is produced, it is necessary to secure the conductive plate 110c produced separately to the inner side of the metal plate 110a which is coated over the overall outer face thereof.
Accordingly, whichever one of the two top plates described above is used, the number of steps increases and the cost increases when compared with those in an alternative case wherein a top plate is produced only by shaping a coated steel plate produced by merely coating an overall outer face of a steel plate. Further, the top plate 110 shown in FIG. 6 has a problem also in that corrosion is liable to occur at joining portions thereof to the conductive plate 110c. 